Process for chroming steel articles



Patented Feb. 4, 1947 UNITED STATES PATENT OFFICE PROCESS roa crmommo STEEL narrows Gottfried Becker, Buderich, near Neuss, and Karl Daeves and Fritz Steinberg, Dusseldorf, Germany; vested in the Alien Property Custodian No Drawing. Application December 6, 1941, Serial No. 421,980. In Germany July 17, 1940 4 Claims. (01. 117-22) be subsequently chromed causes, as is known,'

serious difficulties, as the carbon of the base material forms carbides together with the chromium which diffuses in, said carbides checking the further penetration of the chromium layers.

It was believed that this inconvenience could be sufliciently obviated by increasing the carbon content of the iron to beyond 0.2%. Applicants have, however, ascertained that for proper chroming not only the percentage of the carbon content of the alloys is decisive but also the total quantity of the carbon contained in the steels, in which case not only the quantitative carbon content of the alloys has to be considered but also the cross section of the parts to be treated from which the carbon gets to the surface during the chroming.

As all these measures may cause difllculties, the invention proposes to prevent the influence of the carbon content of the articles to be treated and especially its moving to the surface. Accordingly, the parts to be subsequently chromed are made of so-called alloyed steels.

We have discovered that not all of the known and even the best known alloying elements are in position to check the moving of the carbon during chroming. This carbon movement could not be prevented, for instance, even in the chroming of a basic substance with 0.1% and less carbon and additional 2% of molybdenum. Also in a steel with 0.1% carbon and 3% chromium the carbon moved for instance in the cross section of the basic material in opposition to the diffusion of the chromium, so that also in this instance chromium zones with unsatisfactory phychromed are made of an iron carbon alloy, which k contains in the base material chromium together with other alloying elements, which alone or at least in these percentages have no effect. An addition of 3% chromium alone to a steel with 0:06% carbon cannot stop the carbon movement in the base material. The same is true for a steel which, besides 0.06% carbon and other iron companions, contains alone 0.5% vanadium. By the simultaneous addition of chromium 3% and vanadium 0.5% to the steel, the movement of the carbon is practically absolutely prevented and thereby a chromed surface is produced, which can withstand the highest physical and chemical stressings.

Besides chromium and vanadium, the iron carbon alloy may also contain 0.3 to 3% of molybdenum which can be wholly or partly replaced by tungsten. A steel with carbon 0.12%, chromium, 1.2%, molybdenum 1.2% and vanadium 0.6% can bechromed especially well.

Consequently, the invention relates to a process for the production of articles of iron and steel with corrosion-proof surface by diffusing chromium into the surface at temperatures from about 900 to 1100". The articles to be chromed are made from alloys of iron which contain less than 0.2% carbon, 3 to 4% preferably, of chromlum, 0.3 to 3% of vanadium (preferably 0.5 to

' 1.5% of vanadium), remainder iron and the usual We claim: 1. Process for the production of steel articles with corrosion-proof surfaces by thermal diffusion of chromium into the surfaces consisting in making the articles to be chromed from alloys of iron containing carbon in significant amounts but less than 0.2%, chromium 0.5 to 5%, vanadium 0.3 to 3% and then chroming the articles made of these alloys by such diffusion.

2. Process of claim 1 in which the amount of carbon is 0.1%, chromium 3 to 4% and vanadium 0.3 to 3%.

3. Process of claim 1 in which the alloy also contains molybdenum 0.3 to 3%.

4. Process for the production of steel articles 3 4 with corrosion-proof surfaces by thermal diffusion of chromium into the surfaces consisting in RFFEBENCES CITED making the articles to be chromed from an iron The following references are of record in the alloy containing 0.06% carbon, 3% chromium and file Of this P t nt: gfzucitrxalggmnand then chroming the article 5 UNITED STATES PATENTS GO'I'I'FRIED BECKER". Number Name Date KARL DAEVES. 2,255,482 Daeves se 9, 1941 m Emma 2,157,594 Cooper May 9, 1939 

